The present invention relates to a hydrocarbon reforming apparatus for producing a reformed gas containing hydrogen as a primary component by steam reforming a hydrocarbon stock, and more particularly to a hydrocarbon reforming apparatus suitable for a fuel cell requiring a compact structure and a high heat efficiency.
A reforming apparatus for producing a reformed gas (a combustible gas containing hydrogen as a primary component, carbon monoxide, methane, etc.) by making a mixture of hydrocarbon such as fuel oil, naphtha or natural gas with steam pass a catalyst layer is known from Japanese Patent Laid-open Publication Nos. 53-78992, 53-79766 and 58-63783 and Japanese Patent Publication No. 57-7538, for example.
In the above known reforming apparatus, a reactor tube having a double structure is provided in a reactor. In the double structure, an outer layer portion and an inner layer portion are formed, and they are communicated with each other at upper ends thereof. The outer layer portion is filled with a catalyst to form a catalyst layer. The catalyst in the outer layer portion is heated by a combustion gas flowing along an outer circumferential surface of the reactor tube. A stock gas is supplied to pass through the catalyst layer heated by the combustion gas, so that the stock gas is reformed. Then, a reformed gas thus obtained is discharged through the inner layer portion to the outside of the reactor.
However, the temperature of the combustion gas to be exhausted from the reforming apparatus is remarkably high, and a retention heat of the combustion gas is not efficiently utilized. Further, as the temperature of the reformed gas to be produced is also high, a large heat exchanger for cooling the reformed gas is required. To sufficiently utilize the heat of the combustion gas and the reformed gas until they are discharged from the reforming apparatus, it can be considered that the reactor tube is enlarged in size to increase a heat exchange area of the catalyst layer. However, such a method is not suitable for the reforming apparatus for a fuel cell in particular, which requires a compact structure.